This invention relates to a pressure indicator.
According to a first aspect of the present invention, a pressure indicator comprises a display diaphragm and an indicator diaphragm coupled to and in fluid communication with the display diaphragm and forming a compartment with the display diaphragm; wherein, in use, a change in pressure applied to the diaphragms causes relative movement between the diaphragms which is observable either on the outer surface of the display diaphragm or through the display diaphragm. To see through the display diaphragm effectively, it is preferably transparent.
Preferably, a means to amplify the movement between the diaphragms caused by the change in pressure applied to the diaphragms is provided. This would enable small changes in applied pressure to be observable. The means to amplify the movement between the diaphragms may comprise an article having a first surface and a second surface, the second surface having a larger cross sectional area than the first surface, the first surface being in fluid communication with one of the diaphragms. A change in pressure applied to the second surface causes an amplified movement of the first surface which is communicated to the diaphragms. Preferably, the first surface of the article is the indicator diaphragm.
Preferably, the means to amplify the change in pressure applied to the diaphragms is biased so that on removal of the change in pressure applied, the means to amplify the change in pressure returns to its original position i.e. that prior to the application of the pressure. This ensures that an accurate indication of the pressure is obtained. The biasing means may be a spring or elastomeric material.
In a preferred embodiment, the diaphragms form a compartment and contain a liquid or gel which may be at least partially opaque. The compartment may be sealed, alternatively the diaphragms may be in mechanical communication without being sealed.
In another preferred embodiment the indicator diaphragm bears a recognisable configuration or patt rn such that the configuration or pattern is observable either on the outer surface of the display diaphragm or through the display diaphragm thereby aiding observation of the relative movement. The recognisable configuration or pattern may comprise a symbol or graphic projecting from the surface of the indicator diaphragm. This facilitates observation on the outer surface of the display diaphragm if the symbol or graphic either abuts the inner surface of the display diaphragm or protrudes through the display diaphragm.
Alternatively, either the display diaphragm or, if present, the liquid or gel may be partially opaque. Upon relative movement between the diaphragms, the symbol or graphic which projects from the surface of the indicator diaphragm either appears or disappears or, alternatively, becomes more or less visible when viewed through the display diaphragm.
In order to indicate a range of pressure, it is necessary to define the two extremes of that range, i.e. a high pressure extreme and a low pressure extreme. Thus, it is preferable that the configuration or pattern comprises at least two components, each component corresponding to a different pressure.
Such components may project from the surface of the indicator diaphragm by different amounts, thereby abutting the display diaphragm at different pressures. Alternatively, the components may have different visibility such that they can become visible and invisible at different pressures, e.g. by having different colours or symbols and patterns.
The relative movement of the diaphragms may be accommodated where either diaphragm comprises a flexible polymer and especially an elastomer. The symbol or graphic may also comprise a flexible polymer or elastomer.
Where the indicator diaphragm is subjected to a higher pressure than the display diaphragm, it is preferable that the indicator diaphragm is impermeable so as to prevent leakage.
According to a second aspect of the present invention, apparatus comprises a fluid reservoir and a pressure indicator according to any preceding claim wherein one of the diaphragms is in fluid communication with the fluid reservoir. The apparatus may be an inflatable such as a tyre or a ball.
Th pr ssure indicator may be incorporat d in the surface of the fluid reservoir or, more conveniently housed in or around a valve assembly.
According to a third aspect of the present invention, a method of indicating either fluidic or mechanical pressure comprises the steps of applying a pressure to a pressure indicator, the indicator comprising a display diaphragm and an indicator diaphragm coupled to and in fluid communication with the display diaphragm; and observing the relative movement between the diaphragms caused by the pressure applied, either on the outer surface of the display diaphragm or through the display diaphragm.
Preferably, the indicator diaphragm bears a recognisable configuration or pattern such that the relative movement is observed either when the pattern or configuration abuts the display diaphragm, or when the pattern or configuration becomes visible through the display diaphragm.
In a preferred method, the pattern or configuration may comprise a symbol or graphic having at least two components where each component corresponding to a different pressure. This enables a pressure range to be defined whereby one of the components defines a lower relative pressure, the other a higher relative pressure.